EFFECT OF Mo AND Cr ON THE FRACTURE TOUGHNESS AND FATIGUE CRACK GROWTH RESISTANCE OF A COMPLEX-PHASE C-Mn-V STEEL
Leonardo Barbosa Godefroid1; Ana Paula da Silva Lima1; Tamara Caroline Guimarães Vilela1; Charles de Abreu Martins2; Nina Fonstein2
1 UFOP; 2 ArcelorMittal
doi:10.20906/CPS/COB-2015-0902
Resumo
Automotive industry has demanded the development of new steels with good formability and high strength, aiming to obtain smaller thickness without performance loss, mainly concerning about safety and comfort of the passengers, and to obtain automobile weight reduction. The main challenges to develop these steels are not only to reach the traditional mechanical properties requirements, but also satisfy the additional requirements such as fracture toughness and fatigue crack growth resistance. This work shows results about J integral resistance curves and da/dN-deltaK curves of a C-Mn-V steel, and compare its performance in function of 0.50%Cr and 0.25%Mo additions (wt%). The presence of Cr or Mo in C-Mn-V steel changed its microstructure and, of course, their mechanical properties. Microstructural analysis showed the absence of pearlite on all steels, and the effect of Cr and Mo on increasing the presence of acicular ferrite, bainite and martensite. There has been an increase of martensite, rising from 30% in the C-Mn-V steel to 65% in the steel with 0.50%Cr and 70% in the steel with 0.25%Mo. It has not been verified the presence of precipitates. The addition of Cr and Mo increased the tensile mechanical strength and hardness of the C-Mn-V steel. On the other hand, regarding fracture toughness, the presence of these alloying elements decreased the cracking resistance, mainly for the 0,25%Mo steel. With respect to fatigue, the three steels presented a similar performance. There is only a decrease in the fatigue cracking resistance for the steel with 0.25%Mo in the region I of crack growth (deltaKth region).
Palavras-chave: Fracture toughness; Fatigue crack growth resistance; Complex-phase steels; Effect of alloying